1. Field of the Invention
This technology is applied to a node provided on a ring network.
Among technologies for transmitting data on a ring network that focus on a failure-recovery function is Resilient Packet Ring (RPR). The RPR is a standard set by the Institute of Electrical and Electronics Engineers (IEEE) 802.17 Working Group. RPR is a technology relating to a node on a two-way network using a dual ring network.
Specifically, RPR has the following features.
(a) High-Speed Failure Recovery (failure-recovery ability of 50 msec or less, which is approximately the same level as that of Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH).
(b) Effective Use of Band (effective use of a band thanks to “spatial reuse”)                A token is used as an access control system in a data link such as Fiber-Distributed Data Interface (FDDI) and Token Ring, so only a node that holds the token is able to transmit data. On the other hand, spatial reuse allows data transmission at any time if the link band is available.        
(c) Fairness Function (securing of band fairness using a fairness algorithm)                An available band between nodes on an RPR ring is fairly controlled when congestion occurs. Quality of Service (QoS) is provided using data transfer control that is matched with three priority classes.        
(d) Topology Discovery Function (recognizing the initial state of the ring topology/detecting a variation)                Information (topology database) on a route on the ring network is exchanged between nodes using a control frame.        
(e) Support for Layer 2 Media Access Control (MAC)                RPR corresponds to the MAC sublayer of Layer 2 and uses the MAC technology of Layer 2 to realize a band-sharing ring topology. While the MAC function of RPR is different from that of Ethernet (registered trademark), both can use the same MAC address.        
(f) Use of Existing Technologies for Layer 1 (use of SONET/SDH, Giga bit Ethernet (GbE; registered trademark), 10 GbE)                Data transfer system that is not dependent on a physical layer system is realized.        
When IEEE 802.17-based nodes each having the above-mentioned features communicate with devices (hereinafter referred to as “remote nodes”) subordinate thereto, they always perform flooding all over the RPR ring because they do not have information on the route to the destination remote node. Thus, effective use of the transmission band (spatial reuse) has not been done.
2. Description of the Related Art
Disclosed as a related art using the standard IEEE 802.17 is Laid-open Japanese Patent Application Number No. 2004-242194.
According to the above-mentioned related art example, IEEE 802.17b is a revision of IEEE 802.17 for the purpose of solving the above-mentioned problem. IEEE 802.17b is provided with Spatially Aware Sublayer (SAS) that a technology for transmitting a packet to only a part of the ring rather than to all over the ring, so as to save the band. SAS is a standard for bridging the layer 2 to realize spatial reuse of the ring band. Thus, IEEE 802.17b requires that nodes each have a route table regarding subordinate nodes thereof, that is, remote nodes. This enables each node to perform a unicast communication even with a remote node, thereby enabling effective use of the transmission band (spatial reuse).
Incidentally, if an IEEE 802.17b-based node(s) may be added to a ring network including IEEE 802.17-based nodes or if an IEEE 802.17-based node(s) is updated to an IEEE 802.17b-based node(s), an IEEE 802.17-based node(s) and an IEEE 802.17b-based node(s) may be mixed on the ring network. If remote nodes subordinate to IEEE 802.17-based nodes communicate with one another in such a mixed configuration, flooding is performed, resulting in a problem of consuming the band unnecessarily.